When applied properly and allowed to dry, contact adhesive provides a permanent bond between a variety of surfaces. When using contact cement, you should apply enough cement to coat the surface evenly with it thick enough that a tacky film is left over. However, it's not always possible to apply a perfect coat, and it may sometimes be necessary to thin the contact adhesive, so you should know your options for doing so.
Most contact cement manufacturers recommend using a commercial brand of thinner to thin contact adhesive because these thinners are fairly easy to use, but most contact cement manufacturers offer cement thinners of the same brand name. Using the same brand of thinner as your contact adhesive or a thinner that your contact adhesive manufacturer recommends will ensure that you avoid potential problems that can occur when thinning contact adhesive, such as changing the adhesive's drying time or spray- or brush-ability.
Always follow all the instructions on adhesive thinner labels, which will tell you how much thinner to apply, when to apply it and how to apply it. Also take the recommended precautions, like applying the thinner in a well-ventilated area.
Your first inclination may be to thin contact adhesive with water because water is inexpensive and readily available; however, LePage for Canada does not recommend thinning adhesive with water because water may react negatively with your contact adhesive.
You should also never use lacquer thinners to thin contact adhesive, because the substances are not compatible and may produce harmful fumes. However, Breeding Insulation advises that you can sometimes use lacquer thinner to clean up contact adhesive drips.